Engine cooling thermostat, how does it work

[MapisM]

As per title, I'd be interested to hear more about the thing. For instance...
- the typical operating temperature
- if it works as on/off (I mean, open/close) or gradually
- where along the cooling circuit it's normally placed
- how reliable it is, and if it's supposed to be replaced every X hours and/or Y years

I'm talking of diesel engines, if that matters.
And I appreciate that there might be differences between engines/brands - feel free to mention any.
TIA!

 

[Portofino]

Here you are
https://axleaddict.com/auto-repair/car-thermostat-troubleshooting

Idea is the circulate the closed cooling water around the block only when the engine is cold to speed up it reaching operating temp .
Then the wax gradually expands as the water heats up and the valve opens say @80 degrees ?.In a car coolants is diverted to a radiator and the air / fans / fwd motion cool .In a boat close coolant is diverted to the sea water heat exchanger. Here seawater is used to cool .
In a boat there are TWO water pumps .
One usually a metal impeller circulates the closed circuit and the other water pump is the seawater circulation, that’s the one with a rubber impeller.
Theses two can be gear driven or belt driven or a combo of the two .With my MAN s the seawater is gear driven with a rubber impeller that’s a service item and the closed circuit belt driven with a metal impeller that’s not a service item .
The service item is the belt which needs the correct tension .
This belt also turns the alternator.If it slips then not only the V kicked out by the alternator drop ,the coolant circulation drops off too. That could mask thermostat issues if there are any ?

-Operating opening temp approx 80 degrees its normally stamped on somewhere.

- they can stick either open or closed .Theres normally a small hole in the primary seal that allows a bit through if stuck shut , You will start to overheat .

They are located ( MANs ) at the header tank front side ( opposite to G box ) near the water pump .
You need to dismantle quite a bit normally at least 2 .Irrc mine had 3 in parallel.

There’s no service requirement as such with MAN s but it’s possible when doing a full cooler removal of the charge air and the seawater for stripping and cleaning “while they are in “ in a refresh gaskets kinda way remove the header tank to access them .
As they are a peanuts cost wise in the bigger scheme of the £1000 ,s xX invoice may as well opt to replace .


Volvos the KAD series sit on top at the pulley end ( front) in a easy to access place to the rhs of the strainer iirc ?
They can be removed without any significant strip down , well done Volvo on that one .

 

[Portofino]

Returning to the KAD series Volvo , When it was time to offload the boat I took the T stats out .
This is because the coolers where getting ready for a major overhaul it starting was running hot ish at normal 3000/ 3200 rpm or what ever.

So at the sea trial the buyers surveyors and buyer did not pick up on that as in fact they ran slightly cool .
This is because in the 20 mins 1/2 hour or so even with short stint at WOT there was max diversion to the seawater heat exchanger.
The tell tale is running in the marina they over cool down .Guess they were fixated only on overheats

It’s called “deferred maintenance “the buck was passed on :encouragement:

 

[Greg2]

Returning to the KAD series Volvo , When it was time to offload the boat I took the T stats out .
This is because the coolers where getting ready for a major overhaul it starting was running hot ish at normal 3000/ 3200 rpm or what ever.

So at the sea trial the buyers surveyors and buyer did not pick up on that as in fact they ran slightly cool .
This is because in the 20 mins 1/2 hour or so even with short stint at WOT there was max diversion to the seawater heat exchanger.
The tell tale is running in the marina they over cool down .Guess they were fixated only on overheats

It’s called “deferred maintenance “the buck was passed on :encouragement:

Not that it is likely but remind me never to buy a boat from you Porto!
Perhaps I am the one out of synch but I tend to ensure that everything is fixed and maintained when selling our boats - use it as a selling point

 

[vas]

fwiw,

my IVECOs thermostat is on the outer side of the liquid coolant heat exchanger, extremely easy to access (but being halfway up the block you tend to loose half the coolant if you try to remove it)
They are stamped 62 or 68 (pretty sure it's 62 though) and they look like any bog standard 70-80s car thermostat.
As part of the heat exchanger maintenance, I removed them, took them home, put them in a small pan and heated them with a decent Hg thermometer in the water, they started opening at said temp and over the next couple of mins with temp rising slowly, they opened fully.
So, they are not on-off, but I doubt it will be easy to get a constant temp that they'll just stay slightly on (unless stuck).

Now, mine looked brand new, but circuit is full of ready mixed coolant and I never had to add any, so I guess if yours is similarly maintained, you wont need to bother with it, just get something else to worry about (if you have to )
Finally mine will most likely fail closed I recon judging from my cars of the era. Newer ones fail open (like wife's Sei) but not bothered removing it so no idea how these look like

cheers

V.

 

[MapisM]

As part of the heat exchanger maintenance, I removed them, took them home, put them in a small pan and heated them with a decent Hg thermometer in the water, they started opening at said temp and over the next couple of mins with temp rising slowly, they opened fully.
So, they are not on-off, but I doubt it will be easy to get a constant temp that they'll just stay slightly on (unless stuck).

Now, mine looked brand new, but circuit is full of ready mixed coolant and I never had to add any, so I guess if yours is similarly maintained, you wont need to bother with it, just get something else to worry about (if you have to )

Haha, nope, I've already had my fair share of opportunities to worry about this and that!
Interesting to hear that the thermostat is practically on/off, aside from the short time it takes to fully open (and I suppose also to fully close), when temp goes down again.

So, just to double check, is my understanding correct that the thermostat has bugger all to see with the raw water, which goes through all its intended routes regardless of engine temp? I mean, does raw water always pass through heat exchanger/aftercooler/gearbox HE/manifolds (and eventually expelled, mixed with the exhaust) regardless of any temperature?

 

[MapisM]

In a boat there are TWO water pumps.
One usually a metal impeller circulates the closed circuit and the other water pump is the seawater circulation, that’s the one with a rubber impeller.
Theses two can be gear driven or belt driven or a combo of the two .With my MAN s the seawater is gear driven with a rubber impeller that’s a service item and the closed circuit belt driven with a metal impeller that’s not a service item .
The service item is the belt which needs the correct tension.
This belt also turns the alternator. If it slips then not only the V kicked out by the alternator drop ,the coolant circulation drops off too.

I'm surprised to hear than MAN went that route with inline 6 engines.
In my V8 (as well as in any other V engines, afaik) there is a double pulley with separate belts for the alternator and the circulating pump.
Placed BTW on opposite sides, which makes sense for load distribution, I reckon.

 

[vas]

So, just to double check, is my understanding correct that the thermostat has bugger all to see with the raw water, which goes through all its intended routes regardless of engine temp? I mean, does raw water always pass through heat exchanger/aftercooler/gearbox HE/manifolds (and eventually expelled, mixed with the exhaust) regardless of any temperature?

correct!
thermostat basically "blocks" coolant circulation in the engine block until temp is up when it opens up and brings rather cool coolant in the game (since the coolant still in the h/exchanger is going to be at seawater temp...)
simple and efficient system

V.

 

[Portofino]

I'm surprised to hear than MAN went that route with inline 6 engines.
In my V8 (as well as in any other V engines, afaik) there is a double pulley with separate belts for the alternator and the circulating pump.
Placed BTW on opposite sides, which makes sense for load distribution, I reckon.

Load thing is none reason , belts can and are v long or v short it’s meaningless, think of a modern poly belt in car .
Any alleged uneven tension / wear is spread with adjusting and idling pulleys .

The main thing with I6 and V m diff is the distance with the in-line is not there compared to a V .
Any how the real clever bit is the concepts .

Ideally pumps on engines need to be belt driven independent bolt on units , like the closed cooling with MANs .

This is because if the shaft seal leaks ( more like when ) you don’t want the leak to get into the engine .

Metal impellers are ok because it’s in the closed theres no chance of hard shaft breaking stuff getting trapped in the vanes .
With the raw water they also can be belt driven bolt ons but crucially with flexible rubber impellers to survive hard stuff that may or may not get in past the strainer.

Or accessory gear driven by a spur set of gears remote and in engineering terms a million miles away from sump oil , which MAN do .

As I think you know MTU do BOTH metal seawater impellered pumps for the raw side as well as closed circuit.
But there’s a flaw in the way they have executed this ———— .

MTU pumps use a bronze impeller like on the MTU engines. For example the MTU series 2000 raw water pumps are notorious for causing damage that could have been prevented. The pumps are built with an external weep hole that lets you know if the water or oil seal is leaking. If the pump is leaking raw water and the problem is not addressed on time, the leaking raw water will corrode and seal the weep hole shut. The leaking raw water will not have an exit now and will start flowing through the oil seal leading to the interior of the engine. Many overhauls have had to been done as a result. Therefore its strongly recommend the inspection of the raw water pump to be done often.

On engines with belt driven pumps like the MTU 183, it is of the upmost importance to perform regular visual inspections. On the MTU 183, the raw water pump and coolant pump are belt driven and since belts crack and stretch, it is critical to have them in good working condition. Due to atmospheric conditions and leaks, the pulleys can also rust and can cause a premature failure of the belts as with VP KAD series.

 

[Rocksteadee]

Returning to the KAD series Volvo , When it was time to offload the boat I took the T stats out .
This is because the coolers where getting ready for a major overhaul it starting was running hot ish at normal 3000/ 3200 rpm or what ever.

So at the sea trial the buyers surveyors and buyer did not pick up on that as in fact they ran slightly cool .
This is because in the 20 mins 1/2 hour or so even with short stint at WOT there was max diversion to the seawater heat exchanger.
The tell tale is running in the marina they over cool down .Guess they were fixated only on overheats

It’s called “deferred maintenance “the buck was passed on :encouragement:

Wouldn’t but a boat from you

 

[Rocksteadee]

fwiw,

my IVECOs thermostat is on the outer side of the liquid coolant heat exchanger, extremely easy to access (but being halfway up the block you tend to loose half the coolant if you try to remove it)
They are stamped 62 or 68 (pretty sure it's 62 though) and they look like any bog standard 70-80s car thermostat.
As part of the heat exchanger maintenance, I removed them, took them home, put them in a small pan and heated them with a decent Hg thermometer in the water, they started opening at said temp and over the next couple of mins with temp rising slowly, they opened fully.
So, they are not on-off, but I doubt it will be easy to get a constant temp that they'll just stay slightly on (unless stuck).

Now, mine looked brand new, but circuit is full of ready mixed coolant and I never had to add any, so I guess if yours is similarly maintained, you wont need to bother with it, just get something else to worry about (if you have to )
Finally mine will most likely fail closed I recon judging from my cars of the era. Newer ones fail open (like wife's Sei) but not bothered removing it so no idea how these look like

cheers

V.

Checking if the Thermostat works by placing in pan of water and heating, I think that the stated temperature is when it reaches fully open

 

[BruceK]

I stand to be corrected but as the wax melts at a certain temp the valve will only open and quite quickly at that temp. My KADs have two thermostats. Partially to cater for water flow I presume but I believe one opens at a slightly lower temp than the other. This I think controls the all on or all off tendency.

I may be talking complete BS here mind, just repeating what I have been informed when I raised a similar question.

 

[markc]

On engines with belt driven pumps like the MTU 183, it is of the upmost importance to perform regular visual inspections. On the MTU 183, the raw water pump and coolant pump are belt driven and since belts crack and stretch, it is critical to have them in good working condition. Due to atmospheric conditions and leaks, the pulleys can also rust and can cause a premature failure of the belts as with VP KAD series.

Thankfully the belts are easy to check and very easy to change too!

 

[jfm]

So, just to double check, is my understanding correct that the thermostat has bugger all to see with the raw water, which goes through all its intended routes regardless of engine temp? I mean, does raw water always pass through heat exchanger/aftercooler/gearbox HE/manifolds (and eventually expelled, mixed with the exhaust) regardless of any temperature?

Exactly correct MapisM. The thermostat only regulates the flow of the jacket water circuit (=freshwater/antifreeze circuit). The raw water circuit is not affected by the thrmostat (though is affected by RPM)

 

[LittleSister]

Perhaps not relevant to mobos, but many sailing craft have direct (seawater) cooled engines, and no freshwater coolant or heat exchanger. The thermostats for direct cooled engines open at a lower temperature to those for indirect (freshwater) cooled engines (even the same model engine). The freshwater cooled ones run at a higher, more efficient temperature, but at that temperature salt etc. is precipitated out of the seawater (and its not pressurised) so they're run cooler. I'm not certain, but IIRC the thermostat for the indirect (freshwater) cooled version of my engine (Bukh 36) opens at 90 degrees, whereas the thermostat for the direct (seawater) cooled version opens at 75 degrees. It doesn't pay to have the wrong thermostat!

 

[MapisM]

Perhaps not relevant to mobos, but many sailing craft have direct (seawater) cooled engines

Interesting. I wasn't aware of raw water cooled diesels.
That is a rather common solution in petrol engines though, albeit only up to a point.
For instance, I've had two boats powered by the Mercury 350 cid small blocks, and they had no closed circuit.
But my 496HO powered boat did have it, as well as higher power engines do, all the way up to the 552 cid 1750hp twin turbo monster built by Merc Racing.

All that aside, just for the records, my main reason for posting this thread was a sanity check, sort of.
In fact I found myself wondering, while flushing the engines with fresh water the day after I used the boat (hence with cool engines), whether by running them at idle for a short time I would really flush the whole raw water circuit or not.
Reason being that reaching the operating temperature at idle with no load is almost impossible, or would take forever anyway.
So, thanks for confirming me that I wasn't missing anything.

Btw, there is actually a partial exception I was already aware of, and which contributed to make me wonder about others, if any.
Just in case anyone is interested, in some MAN engines the aftercooler is split in two parts.
The first (smaller, about 1/3) is filled with cooling liquid, and the second with raw water.
But while the cooling liquid flows at all times, the raw water flow is controlled by a valve which opens only when the turbos begin building up pressure.
The logic is that when running at or just above idle it's actually better to warm up a bit the air, rather than cool it down.
So, in these engines, the raw water section of the aftercooler can only be flushed with fresh water when the engine is spinning at 1500+ rpm, which requires a pretty high capacity of fresh water supply, possibly unavailable when flushing the engine.

Actually, there is a trick for letting fresh water flow also in the raw water section of the aftercooler, even with the engine running at idle.
That's another story though, and very engine-specific, so I'm not going to expand further.
Will do if anyone is interested, anyway. :encouragement:

 

[Lon nan Gruagach]

Seems that they are not just open/close...

 

[Portofino]

Interesting.

All that aside, just for the records, my main reason for posting this thread was a sanity check, sort of.
In fact I found myself wondering, while flushing the engines with fresh water the day after I used the boat (hence with cool engines), whether by running them at idle for a short time I would really flush the whole raw water circuit or not.
Reason being that reaching the operating temperature at idle with no load is almost impossible, or would take forever anyway.
So, thanks for confirming me that I wasn't missing anything.
:

Why wait the next day for them to cool ?

Is the sea water too cold or something compared to jetty water ?
What happens at the fuel pontoon temp diff wise ?? Once you have filled up do you wait a day before restarting

All your coolers will drain down within minutes of shut down from seawater and the heat dwell will instantly within crystalline / crystallise any residual dry salt . Raw water runs out because the engines are higher than the WL , well the raw wet able bits are .
By the time you have phaffed with the lines etc at the dock the engines have drained down within minutes of being off ,
“Next day “ or next time you fire up , more so if not left for months on end , a good blast to near WOT will get the raw water dissolving that deposit away .

After a prolonged shut down say 6 weeks I notice a 1 or 2 degree increase in jacket temp during a first hour , @ cruise say 1780 / 1820 rpm .
After an hour that s lost its as if with the raw water pump has blasted sufficiently the inside of the tubes to flush out any deposit from the past 6 weeks that’s sat there kinda Harding up if you like .
Obviously after 1 day or 1 week that slight temp rise does not occur .
This phenomenon is more noticeable after the winter during its first long run out , its as if the shear vol of raw water is giving it a flush .
This year it went from 86/87 to 84/85 within a 2 hr blast on the first run out .

Secondly you have no anodes in any coolers ( because they drain down rendering them useless when shut down ) The anodised corrosion protection is provided by your transom anodes and the earth strap connecting that to the block .I suspect flushing through with fresh water could compromise that protection in any parts that don’t completely drain down as it needs as much electrical continuity as possible for the protective sub atomic particles the Zinc s release to transport to those areas .Residual salt water will do that better .

This whole fresh water flush with a bodged DIY none OEM way in through a hose connection on the strainer with MAN s is nuts .

Go the other way and regularly use them , run them as MAN intended.

 

[jrudge]

My heat exchangers have 2 large anodes each- d12.

They only part drain and when you take them to bits there is a calcium tide mark that eventually blocks the lower half. Fresh flush over winter is worthwhile in my view

 

[Portofino]

With regards attempting to extend the cooler strip down interval by pseudo flushing with fresh water “the day after “.
Over and above my point of a good timely blast of raw seems to do the trick , You are not addressing the oil contamination of the air side fins of the CAC or the film of crud from the closed circuit of the HE .
Or gasket deterioration.

Infact of the two coolers imho it’s actually the charge air coolers fins fouling up that the most serious part .
Fortunately I can access inlet air temp / charge air temp .
Any rise in inlet air temp has an immediate knock on effect on the EGTs .
This is often overlooked as folks get fixated ( correctly and understandably) with fouling when thinking about overloading mitigation tactics .